U.S. patent application number 13/349759 was filed with the patent office on 2012-08-16 for crash can made of aluminum-alloy casting.
This patent application is currently assigned to MAZDA MOTOR CORPORATION. Invention is credited to Motoyasu Asakawa, Takahiro Kimura, Katsuya Nishiguchi, Nobuyuki Oda, Kojiro Tanaka.
Application Number | 20120205927 13/349759 |
Document ID | / |
Family ID | 46579751 |
Filed Date | 2012-08-16 |
United States Patent
Application |
20120205927 |
Kind Code |
A1 |
Asakawa; Motoyasu ; et
al. |
August 16, 2012 |
CRASH CAN MADE OF ALUMINUM-ALLOY CASTING
Abstract
A crash can is made of aluminum-alloy casting and provided
between a side frame extending in a vehicle longitudinal direction
at a side portion of a vehicle and an end portion of a bumper
reinforcement extending in a vehicle width direction. The crash can
comprises a hollow tube portion extending in the vehicle
longitudinal direction and having a cross-shaped section. At least
one of an outwardly-projecting corner portion and an
inwardly-projecting corner portion of the tube portion is formed by
a groove such that a thickness thereof is thinner than that of the
other portion of the tube portion. Accordingly, an impact which a
vehicle body or a passenger may receive in a vehicle collision can
be reduced by the crash can.
Inventors: |
Asakawa; Motoyasu;
(Hiroshima, JP) ; Nishiguchi; Katsuya; (Hiroshima,
JP) ; Kimura; Takahiro; (Hiroshima, JP) ; Oda;
Nobuyuki; (Hiroshima, JP) ; Tanaka; Kojiro;
(Hiroshima, JP) |
Assignee: |
MAZDA MOTOR CORPORATION
Hiroshima
JP
|
Family ID: |
46579751 |
Appl. No.: |
13/349759 |
Filed: |
January 13, 2012 |
Current U.S.
Class: |
293/132 |
Current CPC
Class: |
B60R 19/34 20130101 |
Class at
Publication: |
293/132 |
International
Class: |
B60R 19/34 20060101
B60R019/34 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2011 |
JP |
2011-028172 |
Claims
1. A crash can made of aluminum-alloy casting which is provided
between a side frame extending in a vehicle longitudinal direction
at a side portion of a vehicle and an end portion of a bumper
reinforcement extending in a vehicle width direction, comprising: a
hollow tube portion extending in the vehicle longitudinal direction
and having a cross-shaped section, wherein at least one of an
outwardly-projecting corner portion and an inwardly-projecting
corner portion of the tube portion is formed such that a thickness
thereof is thinner than that of the other portion of the tube
portion.
2. The crash can made of aluminum-alloy casting of claim 1, wherein
a flat portion of said tube portion which is formed between a pair
of outwardly-projecting corner portions which are adjacently
positioned or between the outwardly-projecting corner portion and
the inwardly-projecting corner portion which are adjacently
positioned is formed such that a thickness of part of the flat
portion is thinner than that of the other part of the flat
portion.
3. The crash can made of aluminum-alloy casting of claim 1, wherein
said thinner-thickness forming is achieved by forming a groove
extending in the vehicle longitudinal direction on an outer face or
an inner face of said tube portion.
4. The crash can made of aluminum-alloy casting of claim 2, wherein
said thinner-thickness forming is achieved by forming a groove
extending in the vehicle longitudinal direction on an outer face or
an inner face of said tube portion.
5. The crash can made of aluminum-alloy casting of claim 1, wherein
said thinner-thickness forming is achieved by making said tube
portion in such a manner that the thickness thereof changes
continuously.
6. The crash can made of aluminum-alloy casting of claim 1, wherein
said tube portion is formed in a tapering shape such that a front
portion thereof is slender compared to a rear portion thereof.
7. The crash can made of aluminum-alloy casting of claim 2, wherein
said tube portion is formed in a tapering shape such that a front
portion thereof is slender compared to a rear portion thereof.
8. The crash can made of aluminum-alloy casting of claim 3, wherein
said tube portion is formed in a tapering shape such that a front
portion thereof is slender compared to a rear portion thereof.
9. The crash can made of aluminum-alloy casting of claim 5, wherein
said tube portion is formed in a tapering shape such that a front
portion thereof is slender compared to a rear portion thereof.
10. The crash can made of aluminum-alloy casting of claim 1,
wherein the aluminum-alloy casting has a mechanical property that a
0.2% proof stress is 70 MPa or greater, a tensile strength is 120
MPa or greater, and an elongation is 10% or greater.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a crash can which is made
of aluminum-alloy casting for a vehicle.
[0002] Vehicles are equipped with an impact absorption device to
ensure the safety of passengers or reduce damages of a vehicle body
in a vehicle collision against another vehicle or any obstacle,
such as a building, due to driving mistakes. A crash can (box) is
known as a representative impact absorption device, which is
provided between a bumper reinforcement provided inside a bumper of
the vehicle and an end portion of a side frame of the vehicle
body.
[0003] The above-described crash can, which is generally made of
steel, crashes in a vehicle longitudinally direction in bellows
shape with buckling deformation in a vehicle frontal collision or a
vehicle offset collision, and thereby absorbs a collision energy.
The conventional crash can made of steel is formed by a pair of
inside and outside members which have a U-shaped section,
respectively, and connected to each other so as to provide a hollow
tube shape. It is also known that the closed cross section of this
crash can is formed in a cross shape or a tumbler shape, or it is
formed to have beads at its inside wall face and its outside wall
face. US patent application publication No. 2010/066124, for
example, discloses the crash can made of steel and having the
closed cross section formed in the cross shape, in which the
concave portion provided at the front end face of the crash can
engages with the convex portion having the U-shaped section which
is formed at the rear face of the bumper beam to extend in the
vehicle width direction.
[0004] It is also known that the crash can is made of aluminum
alloy. Japanese Patent Laid-Open Publication No. 2002-39245, for
example, discloses the tube crash can made of aluminum-alloy
casting, in which the wall thickness of the crash can changes
continuously or partially in its axial direction. Further, Japanese
Patent Laid-Open Publication No. 2002-12165 discloses the crash can
made of aluminum-alloy extrusion having the hollow rectangular
section, in which the wall face of the crash can outwardly projects
to provide the convex portion which extends in the axial direction
and have the U-shaped section.
[0005] Further, another structure of the crash can which is
disclosed in US patent application publication No. 2010/0032970 is
also known.
[0006] Herein, the crash can made of aluminum alloy may be
advantageous in providing a lightweight vehicle body, compared to
the one made of steel, despite its wall thickness being relatively
thicker to ensure the proper strength. However, in the case of the
crash can made of aluminum-alloy extrusion, the same sectional
shape basically extends over a whole length of the crash can in the
axial direction. Accordingly, it may be difficult to change the
sectional shape of the crash can made of aluminum-alloy extrusion
in the axial direction in order to effectively obtain the impact
absorption function or provide connecting flanges at both ends.
Meanwhile, in the case of the crash can made of aluminum-alloy
casting disclosed in the above-described second patent publication,
while the wall thickness of the tube portion may be possibly
changed or the flanges may be possibly provided, it has been
desired to obtain the further effective impact-absorption
function.
[0007] That is, when the collision load is added to the crash can,
the crash can resists against the collision load, so that the load
received by the vehicle body may increase until the buckling
deformation occurs initially. Then, the load may decrease in
accordance with the occurrence of the buckling deformation. Thus, a
so-called initial peak may occur. After the crashing of the crash
can caused by this initial buckling deformation, the crash can may
not provide any effective absorption effect of the collision
energy. Consequently, the damages received by the vehicle body and
the impact received by passengers may become improperly large.
[0008] Even in a case in which the crashing of the crash can is not
caused by the initial buckling deformation, the load received by
the vehicle body may increase until the next buckling deformation
occurs. Accordingly, if the subsequent buckling deformations do not
happen properly continuously after the initial buckling
deformation, the effective absorption of the collision energy may
not be achieved, so that the impact received by the vehicle body
may be improperly large.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide a crash can
made of aluminum-alloy casting which can effectively absorb the
collision energy, thereby reducing the damages received by the
vehicle body or the impact received by passengers.
[0010] According to the present invention, there is provided a
crash can made of aluminum-alloy casting which is provided between
a side frame extending in a vehicle longitudinal direction at a
side portion of a vehicle and an end portion of a bumper
reinforcement extending in a vehicle width direction, comprising a
hollow tube portion extending in the vehicle longitudinal direction
and having a cross-shaped section, wherein at least one of an
outwardly-projecting corner portion and an inwardly-projecting
corner portion of the tube portion is formed such that a thickness
thereof is thinner than that of the other portion of the tube
portion.
[0011] That is, the buckling deformation which occurs at the tube
portion when the collision load acts on the crash can is a
phenomena in which the wall of the tube portion deforms laterally
(in a direction perpendicular to the vehicle longitudinal
direction) when the load has reached a limit value. Briefly
speaking, the collision load causes a force to deform a peripheral
wall of the tube portion inwardly or outwardly. In a case in which
the tube portion is formed to have the cross-shaped section, an
outward force acts on one pair of four projecting portions of the
tube portion, while an inward force acts on the other pair of four
projecting portions of the tube portion (herein, each of the pairs
of four projecting portions comprises two projecting portions which
are positioned so as to oppositely face to each other).
[0012] The corner portions of the tube portion of the crash can
according to the present invention are formed such that the
thickness thereof is thinner. Accordingly, the tube portion can
easily deform such that bending of the corner portions is returned
so as to stretch by the above-described inward or outward forces.
This means that when the outward force acts on the above-described
one pair of four projecting portions, the bending of the corner
portions of these projecting potions stretches, so that the width
of the tip of these projecting portions becomes narrower and these
projecting portions can easily deform so as to project outwardly.
Meanwhile, when the inward force acts on the above-described other
pair of four projecting portions, the bending of the corner
portions of these projecting potions stretches, so that the width
of the tip of these projecting portions becomes wider and these
projecting portions can easily deform inwardly. That is, the
above-described thinner-thickness forming of the corner portions
causes the buckling deformation in which the width of the tip of
the one pair of projecting portions becomes narrower and these
projecting portions easily deform so as to project outwardly, while
the width of the tip of the other pair of projecting portions
becomes wider and these projecting portions easily deform so as to
project inwardly.
[0013] Thus, the tube portion of the crash can has the buckling
deformation along with the outward deformation of the one pair of
four projecting portions and the inward deformation of the other
pair of four projecting portions. When the projecting portions
deform outwardly or inwardly and thereby the tube portion has the
buckling, a force to deform the projecting portions in a reverse
direction (inwardly or outwardly) acts on a portion adjacent to the
buckling portion in the vehicle longitudinal direction. That is, at
this moment, the tube portion has the buckling deformation along
with the inward deformation of the one pair of four projecting
portions having the wide tip's width and the outward deformation of
the other pair of four projecting portions having the narrow tip's
width. In this case as well, since the corner portions of the tube
portion are formed such that the thickness thereof is thinner
relatively, the buckling deformation in the same manner can easily
occur.
[0014] As described above, in the case of the crash can according
to the present invention, when the collision load is added, a first
buckling deformation pattern in which the above-described one pair
of projecting portions deforms outwardly and the above-described
other pair of projecting portions deforms inwardly, and a second
buckling deformation pattern in which the one pair of projecting
portions deforms inwardly and the other pair of projecting portions
deforms outwardly occur repeatedly in the vehicle longitudinal
direction, so that the tube portion deforms (crashes) in the
bellows shape. Herein, since the tube portion is formed to have the
above-described relatively-thinner corner portions, the
above-described buckling deformation along with the repeated first
and second deformation patterns can smoothly occur. Thereby,
according to the present invention, the collision energy can be
effectively absorbed, so that the damages received by the vehicle
body or the impact received by passengers can be properly
reduced.
[0015] According to an embodiment of the present invention, a flat
portion of the tube portion which is formed between a pair of
outwardly-projecting corner portions which are adjacently
positioned or between the outwardly-projecting corner portion and
the inwardly-projecting corner portion which are adjacently
positioned is formed such that a thickness of part of the flat
portion is thinner than that of the other part of the flat portion.
Thereby, the flat portion between the corner portions can easily
have the buckling deformation, so that the above-described outward
deformation of the projecting portions having the narrow tip's
width and the above-described inward deformation of the projecting
portions having the wide tip's width can easily occur. That is, the
buckling deformation along with the first and second deformation
patterns can smoothly occur.
[0016] According to another embodiment of the present invention,
the thinner-thickness forming is achieved by forming a groove
extending in the vehicle longitudinal direction on an outer face or
an inner face of the tube portion. Thereby, the groove causes the
tube portion to deform easily, so that the buckling deformation
along with the first and second deformation patterns can smoothly
occur.
[0017] According to another embodiment of the present invention,
the thinner-thickness forming is achieved by making the tube
portion in such a manner that the thickness thereof changes
continuously. Thereby, the buckling deformation along with the
first and second deformation patterns can smoothly occur as
well.
[0018] According to another embodiment of the present invention,
the tube portion is formed in a tapering shape such that a front
portion thereof is slender compared to a rear portion thereof.
Thereby, the buckling deformation of the tube portion starts from
its front end side, and then the buckling deformations along with
the first and second deformation patterns repeatedly occur.
Accordingly, the deformation (crash) in the bellows shape can
smoothly occur.
[0019] Herein, it may be preferable that the aluminum-alloy casting
making the crash can have a mechanical property that a 0.2% proof
stress is 70 MPa or greater, a tensile strength is 120 MPa or
greater, and an elongation is 10% or greater.
[0020] Other features, aspects, and advantages of the present
invention will become apparent from the following description which
refers to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is an exploded perspective view showing a
vehicle-body structure of a vehicle front portion according to an
embodiment of the present invention.
[0022] FIG. 2 is a perspective view of a crash can according to the
embodiment of the present invention.
[0023] FIG. 3 is a lateral sectional view of a tube portion of the
crash can.
[0024] FIG. 4 is a sectional view schematically showing a metal
mold for crash-can manufacturing.
[0025] FIG. 5 is a diagram showing a first deformation pattern of
the tube portion of the crash can.
[0026] FIG. 6 is a diagram showing a second deformation pattern of
the tube portion of the crash can.
[0027] FIG. 7 is an enlarged lateral sectional view showing a
deformation manner of the tube portion of the crash can, omitting
illustration of hutching.
[0028] FIG. 8 is a perspective view showing a deformation state of
the tube portion of the crash can.
[0029] FIG. 9 is a graph showing respective load-deformation
properties of an example and a comparative sample of the crash
can.
[0030] FIG. 10 is a lateral sectional view of the crash can
according to another embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Hereafter, preferred embodiments of the present invention
will be descried referring to the accompanying drawings. However,
these embodiments merely show an example of the present invention,
and any application or use of the present invention should not be
limited by these embodiments.
[0032] FIG. 1 is an exploded perspective view showing a
vehicle-body structure of a vehicle front portion. In this figure,
reference character 1 denotes a pair of crash cans which is made of
aluminum-alloy casting, reference character 2 denotes a pair of
front side frames which extends in a vehicle longitudinal direction
at both side portions of a vehicle, and reference character 3
denotes a bumper reinforcement (bumper beam) which extends in a
vehicle width direction. The crash can 1 is provided to
interconnect a front end of the front side frame 2 and an end
portion of the bumper reinforcement 3.
[0033] The front side frame 2, which is a structure body having a
closed cross section and extending in the vehicle longitudinal
direction, is comprised of an inner member 2a having a U-shaped
section and an outer member 2b having a flat plate shape which are
connected to each other. An attaching plate 4 is fixed to a front
end face of the front side frame 2 such that a plate face thereof
faces vehicle forwardly. The bumper reinforcement 3 is comprised of
a front member 3a having a flat plate shape and a rear member 3b
having a U-shaped section which are connected to each other. A
bumper face (not illustrated) is attached to the bumper
reinforcement 3.
[0034] The crash can 1, as shown in FIG. 2, comprises a hollow tube
portion 5 which extends in the vehicle longitudinal direction and
is formed in a tapering shape such that its front portion is
slender compared to its rear portion. At a rear end of the tube
portion 5 is provided a connecting flange 6 which projects
outwardly. The tube portion 5 is formed to have a cross-shaped
section such that it has eight outwardly-projecting corners 5a and
four inwardly-projecting corners 5b as shown in FIG. 3 and
others.
[0035] A lightweight hole 8 opens at a center of a front wall 7
which closes a front end of the tube portion 5 for light weight,
and bolt holes 9 open at four cross-shaped projection portions of
the front wall 7. The front end of the crash can 1 is connected to
the bumper reinforcement 3 by the bolt holes 9. At four corners of
the connecting flanges 6 are formed bolt holes 9, and a rear end of
the crash can 1 is connected to the attaching plate 4 at the front
end of the front side frame 2 by these bolt holes 9.
[0036] Herein, an inner groove 11 which extends in the vehicle
longitudinal direction is formed at an inner face of each of the
outwardly-projecting corner portions 5a of the tube portion 5, so
that the outwardly-projecting corner portions 5a is formed such
that the thickness thereof is thinner than that of the other
portion of the tube portion 5. An outer groove 12 which extends in
the vehicle longitudinal direction is formed at an outer face of
each of the inwardly-projecting corner portions 5b of the tube
portion 5, so that the inwardly-projecting corner portions 5a is
formed such that the thickness thereof is thinner than that of the
other portion of the tube portion 5 as well. Further, the inner
grooves 11 and the outer groove 12 which extend in the vehicle
longitudinal direction, respectively, are formed at a flat portion
5c between the outwardly-projecting corner portions 5a adjacent to
each other in a peripheral direction and a flat portion 5d between
the outwardly-projecting corner portion 5a and the
inwardly-projecting corner portion 5b adjacent to each other in the
peripheral direction, so that the flat portions 5c, 5d are formed
such that the thickness thereof is thinner than that of the other
part of the flat portions 5c, 5d. That is, the two inner grooves 11
are formed at the two flat portions 5c, 5d positioned on the both
side of the inner groove 11 formed at the outwardly-projecting
corner portion 5a, and the two outer grooves 12 are formed at the
two flat portions 5c, 5d positioned on the both side of the outer
groove 12 formed at the inwardly-projecting corner portion 5b.
[0037] Accordingly, the two inner grooves 11 are provided at each
of the flat portions 5c, and the single inner groove 11 and the
single outer groove 12 are provided at each of the flat portions
5d. Each of the two inner grooves 11 at the flat portion 5c extends
in the vehicle longitudinal direction at a specified position which
is located 1/4 of the width of the flat portion 5c away from the
outwardly-projecting corner portion 5a. The inner groove 11 at the
flat portion 5d extends in the vehicle longitudinal direction at a
specified position which is located 1/4 of the width of the flat
portion 5d away from the outwardly-projecting corner portion 5a as
well. The outer groove 12 at the flat portion 5d extends in the
vehicle longitudinal direction at a specified position which is
located 1/4 of the width of the flat portion 5d away from the
inwardly-projecting corner portion 5b.
[0038] [Method of Manufacturing Crash Can]
[0039] It may be preferable that a vacuum casting device with a
mold-fastening force of 500t be used for manufacturing the crash
can 1. FIG. 4 schematically shows a metal mold of the device. In
this figure, reference character 21 denotes a lower mold and
reference character 22 denotes an upper mold, and a cavity for
molding crash can 23 is formed by the both molds 21, 22. Reference
character 24 denotes a core movable plate, at which a core 25 to
form the above-described lightweight hole 8 and cores 26 to form
the above-described bolt holes 9 are provided, respectively.
Reference character 27 denotes a plunger hole in which a plunger
for pouring molten metal reciprocates, and reference character 28
denotes a path of molten metal.
[0040] The tube portion 5 of the crash can 1 is formed in a
tapering shape such that its front portion is slender compared to
its rear portion, and the inner grooves 11 and the outer grooves 12
extend in the vehicle longitudinal direction, respectively.
Therefore, as apparent from FIG. 4, the lower mold 21 and the upper
mold 22 can be constituted as not a split type of mold, but a
simple two-direction pulling type of mold.
[0041] Herein, it may be preferable to use the aluminum alloy
containing Mn: 1.4 w %-1.6w %, Si: 0.2 w %-5.0 w %, Cu: 0.05 w
%-0.35 w %, Mg: 0.1 w %-0.3 w %, Fe: 0.5 w % -0.7 w %, Ti: 0.1 w
%-0.3 w %, and Al of the rest part thereof including as little
impurities as possible. Thereby, the crash can 1 made of
aluminum-alloy casting which has a mechanical property in which a
0.2% proof stress is 70 MPa or greater, a tensile strength is 120
MPa or greater, and an elongation is 10% or greater can be
provided.
[0042] For example, in a case in which by using the aluminum alloy
containing Mn: 1.56 w %, Si: 0.22 w %, Cu: 0.05 w %, Mg: 0.16 w %,
Fe: 0.65 w %, Ti: 0.15 w %, and Al of the rest part thereof
including as little impurities as possible, the casting is
conducted on condition of a plunger speed: 1.50 m/sec, a
cavity-inside vacuum: 98 kPa, and a mold temperature:
150-160.degree. C., the crash can 1 made of aluminum-alloy casting
which has the mechanical property in which the 0.2% proof stress is
100 MPa, the tensile strength is 220 MPa, and the elongation is
about 80% can be provided.
[0043] [Crashing Deformation of Crash Can]
[0044] When the collision load is added to the crash can 1 via the
bumper reinforcement 3, the tube portion 5 starts its buckling
deformation with a first deformation pattern T1 shown by a solid
line in FIG. 5 and a second deformation pattern T2 shown by a solid
line in FIG. 6 which occur repeatedly in the vehicle longitudinal
direction from an initial sate having its basic sectional shape
"cross shape" BF shown by a two-dotted broken line in FIG. 5. In
the first deformation pattern T1 shown in FIG. 5, upper and lower
projecting portions 31, 32 deform outwardly in the vertical
direction with their width becoming narrower, while right and left
projecting portions 33, 34 deform inwardly in the lateral direction
with their width becoming wider. Meanwhile, in the second
deformation pattern T2 shown in FIG. 6, the upper and lower
projecting portions 31, 32 deform inwardly in the vertical
direction with their width becoming wider, while the right and left
projecting portions 33, 34 deform outwardly in the lateral
direction with their width becoming narrower.
[0045] Next, the operations of the inner grooves 11 and the outer
grooves 12 when the tube portion 5 has the buckling deformation
with the above-described deformation patterns T1, T2 will be
described referring to FIG. 7. In this figure, reference character
11A denotes the inner groove formed at the flat portion 5c,
reference character 11B denotes the inner groove formed at the
outwardly-projecting corner portion 5a, reference character 11C
denotes the inner groove formed at the flat portion 5d, reference
character 12A denotes the outer groove formed at the flat portion
5d, and reference character 12B denotes the outer groove formed at
the inwardly-projecting corner portion 5b.
[0046] Herein, when an outward force F1 (acting upwardly in FIG. 7)
is added to the flat portion 5c of the projecting portion 31 due to
the collision load, a bending force acts on the flat portion 5c so
as to convex the flat portions 5c, so that a stress concentrates in
a specified portion of the flat portion 5a which is positioned at
the inner groove 11A. Thereby, this specified portion deforms
easily so as to bend as shown by a two-dotted broken line (the
inner groove 11A.fwdarw.11A').
[0047] When the outward force F1 (upwardly) is added to the flat
portion 5c of the projecting portion 31, an inward force F2 acts on
the flat portion 5d of the projecting portion 31. Herein, since the
outwardly-projecting corner portion 5a of the projecting portion 31
is formed to be thinner by the inner groove 11B, it deforms easily
so as to stretch as shown by the two-dotted broken line in the
figure (the inner groove 11B.fwdarw.11B').
[0048] When the outward force F1 (upwardly) is added to the
projecting portion 31 due to the collision load, a force F3 acting
in the same direction is added to the flat portion 5d of the
adjacent projection portion 34. Consequently, a bending stress
concentrates in a specified portion of the flat portion 5d which is
positioned at the outer groove 12A. Thereby, this specified portion
bends easily as shown by a two-dotted broken line to become an
inwardly-projecting corner (the outer groove 12A.fwdarw.12A').
[0049] Herein, since the inwardly-projecting corner portion 5b
between the projecting portions 31, 34 is formed to be thinner by
the outer groove 12B, it deforms easily so as to stretch as shown
by the two-dotted broken line in the figure due to the inward force
F2 acting on the flat portion 5d of the projecting portion 31 and
the outward force F3 acting on the flat portion 5d of the
projecting portion 34 (the inner groove 12B.fwdarw.12B').
[0050] When the outward force F3 (upwardly) is added to the
projecting portion 34 due to the collision load, an inward force F4
is added to the flat portion 5c of the adjacent projection portion
34. Herein, since the outwardly-projecting corner portion 5a of the
projecting portion 34 is formed to be thinner by the inner groove
11B, it deforms easily so as to stretch as shown by the two-dotted
broken line in the figure due to the forces F3, F4 (the inner
groove 11B.fwdarw.11B').
[0051] As apparent from the above description, when the outward
force is added to the projecting portion, the inner grooves 11A of
the flat portion 5c, the inner groove 11B of the
outwardly-projecting corner portion 5a, and the outer groove 12A of
the flat portion 5d cause the outwardly-projecting deformation
having the narrow tip's width of the projecting portion. Meanwhile,
when the inward force is added to the projecting portion, the inner
grooves 11B of the outwardly-projecting corner portion 5a, the
inner groove 11C of the flat portion 5d, and the outer groove 12B
of the inwardly-projecting corner portion 5b cause the
inwardly-projecting deformation having the wide tip's width of the
projecting portion.
[0052] The repeated occurrences of the above-described first and
second deformation patterns T1, T2 are caused by the occurrences of
the outwardly-deforming force acting on the specified portion
adjacent to the buckling portion when the metal plate is bent
inwardly, for example. As a result, the tube portion 5 of the crash
can 1 deforms (crashes) in the vehicle longitudinal direction in
the bellows shape as shown in FIG. 8.
[0053] Since the tube portion 5 has the cross-shaped section, even
in the case of the vehicle offset collision in which the input
direction of the collision load is offset vertically or laterally,
in addition to the vehicle frontal collision, the cross-shaped
projecting portions 31-34 can support so as to prevent any
falling-down deformation of the tube portion 5. Thereby, the
bellows-shaped deformation (crashing) with the repeated first and
second deformation patterns T1, T2 can be made occur.
[0054] FIG. 9 shows results of crashing test of the crash can made
of aluminum-alloy casting having the cross-shaped section
(load-crashing deformation data). An example has the
above-described inner groove 11 and outer groove 12, while a
comparative sample has no such inner and outer grooves.
[0055] According to the comparative sample, after the load peak
occurs in an initial stage of the collision, the load value
decreases greatly and then stays at a low load value. This
load-deformation property is caused by breakage of the tube portion
due to the initial buckling deformation of the tube portion.
[0056] By contrast, according to the example, the load peak in the
initial stage occurs similarly to the above-described comparative
sample, but the decrease of the load value after the load peak's
occurrence is relatively small and the load value stays at a
relatively high value. This means that the tube portion has
repeated buckling deformations, without being broken by the initial
buckling deformation. This is because the above-described inner and
outer grooves 11, 12 cause the repeated buckling deformations with
the first and second deformation patterns T1, T2. Accordingly, a
substantially flat load-deformation property can be provided. Thus,
according to the present invention, the effective absorption of the
collision energy can be achieved, so that the damages which the
vehicle body may receive or the impact which passengers may receive
can be reduced properly.
[0057] FIG. 10 shows the crash can of another embodiment of the
present invention. In this crash can 1, the eight
outwardly-projecting corner portions 5a and the four
inwardly-projecting corner portions 5b of the tube portion 5 having
the cross-shaped section are formed such that the thickness thereof
is thinner than that of the other portion of the tube portion 5 by
changing their thickness continuously, differently from the
above-described embodiment in which the inner and outer grooves 11,
12 are used. Herein, the flat portions 5c, 5d have no
partially-thinner part thereof.
[0058] Thus, since the eight outwardly-projecting corner portions
5a and the four inwardly-projecting corner portions 5b of the tube
portion 5 are formed such that the thickness thereof is thinner
than that of the other portion of the tube portion 5, these corner
portions 5a, 5b can easily deform so as to stretch from their
initials bending state as well. These corner portions 5a, 5b can
promote the outward projection of the projecting portions 31-34
having the narrow tip's width and the inward projection of the
projecting portions 31-34 having the wide tip's width, so that the
buckling deformation with the repeated first and second deformation
patterns T1, T2 can be provided to the tube portion 5 smoothly.
[0059] The present invention should not be limited to the
above-described embodiments, and any other modifications and
improvements may be applied within the scope of a spirit of the
present invention.
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